Chemicals that are used in the manufacture of semiconductor devices must be maintained at specific pressures and temperatures. In particular, chemicals used for Chemical Vapor Deposition (CVD) processes must be maintained at predetermined conditions. One chemical that is commonly used to form metal tungsten layers using CVD processes is tungsten hexafluoride (WF6). As the tungsten hexafluoride is fed to the CVD chamber, it expands and heats such that it becomes a gas. The temperature and pressure under which a chemical is injected into the CVD chamber are critical to the success of the CVD process. That is, unless the conditions such as temperature and pressure are maintained at the proper levels, failure of the CVD process will result. In addition, the chemical must also be stored at a specific temperature and pressure.
Prior art methods for storing and supplying a chemical to a CVD process typically involves the use of a cylindrical metal bottle to house the chemical. The bottle of chemical is typically placed within a jacket formed by serpentine tubes that run up and down the length of the jacket so as to form a cylindrical enclosure. The bottle is then strapped into the jacket. The jacket is then secured to the back of a gas cabinet. Typically, metal straps are used to rigidly secure the jacket to the back of the gas cabinet.
However, securing the bottle to the jacket makes it rather difficult to monitor the amount of chemical in the bottle since the jacket is attached to the gas cabinet. It is important to monitor the amount of chemical remaining in the bottle in order to ensure that the proper amount of chemical is being delivered to the CVD chamber. It is also important to have accurate, up-to-date information on the exact amount of chemical remaining in the bottle in order to guarantee that there will always be enough chemicals on hand so that the entire CVD processes can successfully be completed. Unless a sufficient amount of chemical remains in the bottle to complete a particular batch of semiconductor wafers, the CVD process may terminate prematurely. In addition, bottles must be removed before the bottle is completely empty (typically at a weight of one pound of chemicals) to prevent unwanted byproducts that may have settled to the bottom of the bottle from being introduced into the CVD process. Premature termination of the CVD process and unwanted byproducts result in semiconductor wafers that are defective and must be thrown away. The entire CVD process must then begin anew, resulting in wasted time and money. Thus, it is important to know the amount of chemical remains in the bottle. Knowledge of the amount of chemical remaining in a bottle is also important for inventory control purposes. More particularly, such knowledge allows an operator to order a new bottle when the amount of chemical in the bottle is low.
Prior art methods for determining the amount of chemical remaining in the bottle involve the use of a scale that is either placed on the floor of the gas cabinet, or is attached to the wall of the gas cabinet a short distance above the floor. When the bottle is place within the jacket, the bottle rests on the scale. However, the attachment of the bottle to the jacket results in the inability to accurately determine the weight of the bottle. This is due to the fact that the jacket is secured to the back of the cabinet. Thus, any determination of weight is inexact.
Further complicating matters is the fact that shut-off systems are attached to the gas bottle for shutting off the flow of chemicals in an emergency. Typically, the shut-off system will include a pneumatic valve that automatically shuts off the flow of chemicals in an emergency. However, in order for the pneumatic valve to work, the bottle must be secured such that it will not rotate. Thus, it is quite important to tightly strap the bottle to the jacket so as to assure that the shut-off system will properly work. Again, this makes it very difficult to accurately measure its weight.
Another problem with this type of prior art system is the time it takes to attach and remove bottles. It takes a significant amount of time to strap a bottle to the jacket. Similarly, unstrapping a bottle from the jacket is time consuming. Thus, the process of replacing bottles is time consuming.
A method and apparatus for storing a bottle of chemical to be used in a CVD process that maintains the chemical at a desired temperature and pressure is needed. In addition, a method and apparatus that allows for the accurate determination of weight is needed. Furthermore, a method and apparatus that will allow for bottles to be easily installed and replaced is needed. The present invention provides a unique, novel, and effective solution that meets all of these needs.